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Abstract

Aperiodic Nanowire (NW) arrays have higher absorption than equivalent periodic arrays, making them of interest for photovoltaic applications. An inevitable property of aperiodic arrays is the clustering of some NWs into closer proximity than in the equivalent periodic array. We focus on the modes of such clusters and show that the reduced symmetry associated with cluster formation allows external coupling into modes which are dark in periodic arrays, thus increasing absorption. To exploit such modes fully, arrays must include tightly clustered NWs that are unlikely to arise from fabrication variations but must be created intentionally.

Figures (4)

Absorption spectra of NW arrays with a = 31 nm, f = 30%, with increasing clustering l = 0.0, 0.2, 0.5, 0.8, 0.95. Inset shows cluster geometry where a is the NW radius, d is the unit cell dimension, g is the gap size between NW surfaces, and t is the distance a NW can be moved before touching its neighbour.

Coupling coefficient (left axis) of the incident plane wave to the fundamental mode (blue upward triangles) and the second bright mode (green downward triangles) versus gap between NW surfaces. The ultimate efficiency η of the clusters is also shown (red circles and right axis).